A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. In recent years, the use of both mobile media and navigation systems in a vehicle has become increasingly more common. Because of data storage requirements, such systems were initially somewhat bulky and required that the systems be permanently installed in the vehicle. However, more recently developed devices are sufficiently compact to allow them to be personally portable and be temporarily mounted within the vehicle. This gives the user the option to use the device both inside and outside of the vehicle.
To have the navigation display visible to the driver when such devices are used within a vehicle, the portable device is either, held by the driver or a passenger, propped up against the interior structure of the vehicle, or otherwise attached to a device mount. Such a device mount typically is further secured to a portion of the interior of the vehicle at a position such that the display is visible by the driver. An example of the attachment of such a device mount to the interior of the vehicle is via a suction cup portion to the front windshield.
To increase the portability of such navigation devices it is desirable to reduce or minimize the overall physical size of the device as much as possible. Of course, the reduction of the overall size of such navigation devices has resulted in a similar reduction in the size of the device components, including the display and the controls. While being used as a portable device, the smaller display and controls tend not to be a problem for the user as the portable device is held relatively close and the user can concentrate primarily on the operation and display of the navigation device.
However, when such a portable navigation device is mounted in a vehicle, the smaller display and controls present certain problems for the driver. One such problems includes being difficult to read or otherwise observe the information on the small display of the portable device, especially given that the driver's primary attention and concentration needs to be directed towards the operation of the vehicle and the road ahead, and not on the navigation display. This problem is compounded by the fact that when attached to a device mount, the navigation device is typically held much further away from the user than if it was held in hand in a portable mode.
Another problem of in-vehicle use is that the controls such as keys and touch panel of the portable navigation device are also positioned relatively far away and are small in size. Yet another problem is that the sounds generated by the portable navigation device, such as directional call-outs, street names and the like, may not be heard by the driver especially due to the distant positioning of the navigation device and the effect of other sources of sound, such as the car audio system.
A portable navigation device may be used in a vehicle in conjunction with an external (second) display device such as a head unit of the vehicle audio/video system. The external display device in general has a larger display size compared to the display size of the portable navigation device. Moreover, the external display device may also be positioned in such a way that the user is able to reach and read or observe the information on the display with ease. Thus, it would be advantageous to connect the portable navigation device to the external display. However, an aspect ratio of the external display may be different from that of the portable navigation device.
Therefore, a need exists for a navigation device which includes a removable navigational unit, which while used in the vehicle, provides for an improved operation of the navigation device within the vehicle. Moreover, there is a need for a method and apparatus of image correction to display image effectively to an external display that takes account of the possible display shape and aspect ratio difference.